Gracilioethers A-C, Antimalarial Metabolites from the Marine Sponge Agelas gracilis Reiko Ueoka, † Yoichi Nakao,* ,¶,† Shizuka Kawatsu, † Junko Yaegashi, † Yoshitsugu Matsumoto, † Shigeki Matsunaga, † Kazuo Furihata, † Rob W. M. van Soest, ‡ and Nobuhiro Fusetani* ,§,† Graduate School of Agricultural and Life Sciences, The UniVersity of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan, and Zoological Museum, UniVersity of Amsterdam, 1090GT Amsterdam, The Netherlands ayocha@waseda.jp; anobu@fish.hokudai.ac.jp ReceiVed February 20, 2009 Three new antiprotozoan compounds, gracilioethers A-C(1-3), have been isolated from the marine sponge Agelas gracilis. Their structures were elucidated on the basis of spectroscopic and chemical methods. Gracilioethers A-C showed antimalarial activity against Plasmodium falciparum with IC 50 values of 0.5-10 µg/mL, whereas gracilioether B (2) also showed antileishmanial activity. Introduction Protozoan infection is increasingly becoming a threat to human beings; for example 300-500 million people are infected by malaria worldwide each year and one to three million die. 1 Numberous attempts including use of the malaria vaccine have been made to control this disease, but the administration of antimalarial drugs is still most effective at this moment. Because of increasing resistance to existing antimalarial drugs, there is an urgent need for the development of antimalarial drugs with new structures and modes of action. Marine natural products have been explored for this purpose, which resulted in the discovery of several drug candidates, including manzamines 2 and cyclic peroxides. 3 In the course of our continuing search for drug leads from Japanese marine invertebrates, we found that the deep-sea sponge Agelas gracilis collected in southern Japan showed considerable antimalarial activity in the lipophilic extract. Bioassay-guided fractionation of the extract afforded three new compounds of the plakortin family named gracilio- ethers A-C. Results and Discussion The CHCl 3 soluble materials of the MeOH extract of the sponge were fractionated by the modified Kupchan procedure 4 to yield hexane, CHCl 3 , and 60% MeOH layers, the last of which was combined with the n-BuOH extract of the water-soluble portion of the MeOH extract and sequentially separated by ODS flash chromatography, gel-filtration, and silica gel open column chromatography. The active fraction was finally purified by * To whom correspondence should be addressed. Y.N.: phone/fax +81-3- 5286-2568. N.F.: phone/fax +81-138-40-8884. † The University of Tokyo. ¶ Present address: School of Advanced Science and Engineering, Waseda University, Tokyo 169-8555, Japan. ‡ University of Amsterdam. § Present address: Graduate School of Fisheries Sciences, Hokkaido Univer- sity, Hakodate 041-8611, Japan. (1) Sachs, J.; Malaney, P. Nature (London) 2002, 415, 680–685. (2) (a) Sakai, R.; Higa, T. J. Am. Chem. Soc. 1986, 108, 6404–6405. (b) Ang, K. K. H.; Holmes, M. J.; Higa, T.; Hamann, M. T.; Kara, U. A. K. Antimicrob. Agents Chemother. 2000, 44, 1645–1649. (3) Kawanishi, M.; Kotoku, N.; Itagaki, S.; Horii, T.; Kobayashi, M. Bioorg. Med. Chem. 2004, 12, 5297–5307. (4) Kupchan, S. M.; Britton, R. W.; Ziegler, M. F.; Sigel, C. W. J. Org. Chem. 1973, 38, 178–179. 10.1021/jo900380f CCC: $40.75  2009 American Chemical Society J. Org. Chem. 2009, 74, 4203–4207 4203 Published on Web 04/29/2009